Since Scout has no mother, Calpurnia takes on the motherly role. Atticus considers her the main authority in his house, and makes his children mind her.

Scout does not always get along well with Calpurnia. She thinks Cal is way too strict.

Our battles were epic and one-sided. Calpurnia always won, mainly because Atticus always took her side. She had been with us ever since Jem was born, and I had felt her tyrannical presence as long as I could remember. (ch 1)

Calpurnia also taught Scout to write, and used it to reinforce Biblical lessons.

In Calpurnia's teaching, there was no sentimentality: I seldom pleased her and she seldom rewarded me. (ch 2)

There's some folks who don't eat like us … but you ain't called on to contradict 'em at the table when they don't. That boy's yo' comp'ny and if he wants to eat up the table cloth you let him, you hear?" (ch 3)

When Scout objects that he’s just a Cunningham, meaning he is poor, she tells Scout that anyone who comes into her house is her company.

Throughout the book, Calpurnia is the voice of reason and a moral presence in Scout’s life. Even though she is black, Scout trusts her and respects her, even if she sometimes finds it hard to live with her.

Calpurnia is the Finch's housekeeper and cook. She is a coloured woman but possesses a good deal of common sense and knowledge. She has been working in the house ever since Jem was born and after Scout's mother dies, she becomes a substitutory disciplinary figure in the house. Atticus knows that Calpurnia is an invaluable teacher to the children, and that is why he refuses to fire her, despite his sister's insistence. Calpurnia is much loved and respected by the two children and she is almost a member of their family. Calpurnia's role is especially invaluable to Scout, who in the absence of any female figure in the household, grows up as a tomboy. Calpurnia's major role in the novel is as a mentor to Scout. In the first chapter Scout introduces her as:

She was all angles and bones. She was near-sighted; she squitned; her hand was wide as a bed slat and twice as hard. She was always ordering me out of the kitchen, asking me why I could not behave as well as Jem when she knew he was older, and calling me home when I wasn't ready to come. Our battles were epic and one-sided. Calpurnia always won, mainly because Atticus always took her side.

When Walter Cunnigham Jr. is invited to lunch at the Finches' and Scout inadvertantly embarrass him, Calpurnia tells Scout:

Hush your mouth! Don't matter who they are, anybody sets foot in this house's yo' comp'ny, and don't you let me catch you remarkin' on their ways like you was so high and mighty! Yo' folks might be better'n the Cunninghams but it don't count for nothin' the way you're disgracin' 'em - if you can't act fit to eat at the table you can just set here and eat in the kitchen!

Her moral lesson to Scout here is to respect people, even if you think you are better than them. According to her, acting like you are better them is the surest way to show that you are not. This dialogue foreshadows Bob Ewell's bad behaviour to the Robinson family, just because they are black, while the truth Tom and Helen Robinson and their children live a more hygenic, independent and god-fearing life, than the Ewells.

Calpurnia was a well-educated woman.

Atticus said Calpurnia had more education than most coloured folks

Miss Maudie Atknison's aunt taught Calpurnia to read and write. However, despite having a better command on language than most of her congregation, she never puts on airs, and instead prefers talkin in broken English or what Scout calls 'nigger-talk' because she does not want her peers to feel that she is putting on airs. Atticus too respects Calpurnia's guiding presence in his children's life and he firmly defends her against his sister Aunt Alexandra.

Anything fit to say at the table's fit to say in front of Calpurnia. She knows waht she means to this family.